Japanese Unexamined Patent Application Publication No. 2015-085887 (Abstract, paragraphs [0023] to [0026]) provides a drive assistance system that moves a vehicle to the leftmost lane by automatic control and then stops the vehicle if an abnormal situation occurs in the health condition of a driver. This system recognizes a lane mark on the left of a travel road on the basis of captured image information of a camera that captures an image at the front of the vehicle if an abnormal situation occurs in the health condition of the driver. Then, the system changes the lane to the left lane by automatic control if the type of the lane mark is a broken line, and stops the vehicle if the type of the lane mark is not a broken line.
The drive assistance system that changes the lane by the recognition of the broken line as a trigger has various problems as follows. When the vehicle is located at a position before a position at which the type of the lane mark is switched from a slid line to a broken line, the drive assistance system provided therein recognizes a broken line ahead of the switching position. For example, if the camera has high detection accuracy or high recognition accuracy, the camera recognizes the broke line at a time point at which a long distance is still left to the switching position. Then, lane change control may be started although the long distance is still left to the broken line. The driver may feel uncomfortable with such a lane change operation.